Move string truncation helpers into codex-utils-string (#15572)

- move the shared byte-based middle truncation logic from `core` into
`codex-utils-string`
- keep token-specific truncation in `codex-core` so rollout can reuse
the shared helper in the next stacked PR

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/core/src/tools/code_mode/mod.rs

@@ -27,11 +27,11 @@ use crate::tools::parallel::ToolCallRuntime;
 use crate::tools::router::ToolCall;
 use crate::tools::router::ToolCallSource;
 use crate::tools::router::ToolRouterParams;
-use crate::truncate::TruncationPolicy;
-use crate::truncate::formatted_truncate_text_content_items_with_policy;
-use crate::truncate::truncate_function_output_items_with_policy;
 use crate::unified_exec::resolve_max_tokens;
 use codex_features::Feature;
+use codex_utils_output_truncation::TruncationPolicy;
+use codex_utils_output_truncation::formatted_truncate_text_content_items_with_policy;
+use codex_utils_output_truncation::truncate_function_output_items_with_policy;
 
 pub(crate) use execute_handler::CodeModeExecuteHandler;
 use response_adapter::into_function_call_output_content_items;

codex-rs/core/src/tools/context.rs

@@ -4,8 +4,6 @@ use crate::codex::TurnContext;
 use crate::tools::TELEMETRY_PREVIEW_MAX_BYTES;
 use crate::tools::TELEMETRY_PREVIEW_MAX_LINES;
 use crate::tools::TELEMETRY_PREVIEW_TRUNCATION_NOTICE;
-use crate::truncate::TruncationPolicy;
-use crate::truncate::formatted_truncate_text;
 use crate::turn_diff_tracker::TurnDiffTracker;
 use crate::unified_exec::resolve_max_tokens;
 use codex_protocol::mcp::CallToolResult;
@@ -16,6 +14,8 @@ use codex_protocol::models::ResponseInputItem;
 use codex_protocol::models::SearchToolCallParams;
 use codex_protocol::models::ShellToolCallParams;
 use codex_protocol::models::function_call_output_content_items_to_text;
+use codex_utils_output_truncation::TruncationPolicy;
+use codex_utils_output_truncation::formatted_truncate_text;
 use codex_utils_string::take_bytes_at_char_boundary;
 use serde::Serialize;
 use serde_json::Value as JsonValue;

codex-rs/core/src/tools/js_repl/mod.rs

@@ -42,12 +42,12 @@ use crate::original_image_detail::normalize_output_image_detail;
 use crate::sandboxing::ExecOptions;
 use crate::tools::ToolRouter;
 use crate::tools::context::SharedTurnDiffTracker;
-use crate::truncate::TruncationPolicy;
-use crate::truncate::truncate_text;
 use codex_sandboxing::SandboxCommand;
 use codex_sandboxing::SandboxManager;
 use codex_sandboxing::SandboxTransformRequest;
 use codex_sandboxing::SandboxablePreference;
+use codex_utils_output_truncation::TruncationPolicy;
+use codex_utils_output_truncation::truncate_text;
 
 pub(crate) const JS_REPL_PRAGMA_PREFIX: &str = "// codex-js-repl:";
 const KERNEL_SOURCE: &str = include_str!("kernel.js");

codex-rs/core/src/tools/mod.rs

@@ -15,9 +15,9 @@ pub mod sandboxing;
 pub mod spec;
 
 use crate::exec::ExecToolCallOutput;
-use crate::truncate::TruncationPolicy;
-use crate::truncate::formatted_truncate_text;
-use crate::truncate::truncate_text;
+use codex_utils_output_truncation::TruncationPolicy;
+use codex_utils_output_truncation::formatted_truncate_text;
+use codex_utils_output_truncation::truncate_text;
 pub use router::ToolRouter;
 use serde::Serialize;